1. Field of the Invention
The invention, as covered by Ref4, Nonprovisional patent application Ser. #09/947240, filed Sep. 05, 2001, entitled Interconnection Devices, generally relates to interconnection devices that make what is referred to as “temporary” interconnections, which are considered non-permanent. It relates more particularly to electrical connectors, sockets, probes, etc., and more particularly relates to high-density electrical connectors used in test and burn-in done on miniaturized electrical components. More details on this are covered in the original Application, Ref4.
The present invention generally relates to what is referred to as “permanent” interconnections, which include solderable interconnections, and/or mounting of electronic components on boards or on substrates, or on other electronic components and the like.
The present invention is presented in two groups, simply to make it easy to follow, although the two groups can be combined under the one category of permanent interconnections.
The first group relates to leaded electronic components, which have already “leads” or “legs”, and/or electronic components that can be provided with leads to make them look as leaded. It mainly covers the leads of such components and the shapes and orientation of these leads, to enhance the performance of such components. This is generally referred to as “permanent” interconnection.
The second group of the present invention covers in particular interconnections between “lead-less” electronic components and boards and/or substrates, or other similar lead-less components. This is also generally referred to as “permanent” interconnection.
The invention utilizes many of the definitions and items described in the referenced provisional applications as well as the referenced patent application, and it expands on them in the section entitled “DEFINITIONS”.
General Background and Prior Art, Applicable to Both Groups:
The important background that is common to both groups is the problems resulting from exposing electronic assemblies to varying temperatures, such as thermal cycling or power cycling, or simply from being exposed to harsh environment, including hot and cold temperature environment or to excessive stresses due to shock and vibration.
In the case of leaded electronic components, the first group, like DIP Packages, it has been know that plastic packages are not as reliable as ceramic packages. Plastic packages do not last as long as Ceramic packages. The Military, the Airline Industry and the Telecommunication Industry require that component last some ten to twenty years without failure. These industries specify ceramic leaded components most of the time, because their experience lead them to believe that ceramic components can satisfy these long operating lives, better than plastic components. It has been stated that one of the reasons why plastic leaded components fail prematurely, as compared to ceramic, beside the fact that the plastic materials themselves are not considered “hermetic”, is the occurrence of micro-cracks between the plastic material and the leads or rather the legs. The legs are made of metal, most of the time out of Alloy 22 or other similar metals, which ideally has a TCE that closely matches the TCE of Silicon. Regardless of the material, the legs are usually relatively stiff. After a component is assembled/soldered to its board, it has been noticed that some micro-cracks develop between the legs and the surrounding plastic material. The cracks start at the outside edges of the plastic, right next to the legs, and gradually the cracks migrate inwards and become larger, until they allow moisture and outside atmospheric gases to migrate inwards also towards the chip inside the package. This migration of undesirable materials can damage the chip or at least can make the chip “age” faster. The end result is the failure of the package. It is also believed that thermal cycling accelerates such micro-cracks. The present invention proposes certain solutions that are believed to be able to improve this situation. These solutions will be described later below.
In the case of leadless electronic components, the second group, like the BGAs and the LCCCs, it has been know for a while that soldering such components directly to substrates or to PCBs is not the right thing to do. It can lead to premature failure. This is especially true, when the component is relatively large, i.e. approx. ¼ inch or larger on the side, and when the material of the component is different than that of the substrate, e.g. when the component is silicon or ceramic, while the substrate is FR4, and when the temperature can vary considerably during the life of the assembly. For this reason, several designs have been proposed in the past to counteract the unfavorable effect of such conditions. For example, the inventor, Gabe Cherian, together with other co-inventors, had invented what was called “CCMD”, Chip Carrier Mounting Device, which was later called “Solder Columns” or “Solder Quick”. This is covered by U.S. Pat. Nos. 4,664,309, 4,705,205 and 4,712,721. Other attempts have been made by other inventors, which were more or less successful.
The additional problem nowadays is the fact that many of the components are being miniaturized. The center distances between contact pads are getting smaller and smaller, and the old inventions can no longer keep up with such miniaturization. For example, BGAs have center distances down to 0.020″ (approx. 0.5 mm) and when we consider Chip Scale Packaging, the center distances can be even smaller. The Cherian Solder Columns were originally designed and built to work with 0.050″ (approx. 1.25 mm) center distances. Cherian Solder Columns cannot readily be simply scaled down to size. For this reason, the present invention has addressed this problem and offers solutions as will be described later.
For the purpose of the following invention description, I will use certain words or terms that may be peculiar to this application. They will be explained in the following definitions, or as I go along during the application.
Standard Integrated Circuit Packages:
LCCC: Leadless Ceramic Chip Carrier
BGA: Ball Grid Array Package
PGAP: Pin Grid Array Package
SIP: Single In-Line Package
Bending or Flexing Leads Across Flats, Across Face, Across Edge:
FIG. 1 shows two leads at a corner of a leaded package. Usually the leads of leaded electronic devices are made out of flat sheet metal, with a relatively small thickness compared to the width of the lead. The lead 101 on the right hand side of the figure is being bent “across the flats” or “across the face”. This is my definition. It implies that the flat wide section of the lead is facing the bending direction 103 and 105. The lead 107 on the left-hand side of the figure is being bent “across the edge”. This definition implies that the bending direction 109 and 111 is against the edge of the lead.
Lead Nomenclature, include the following, see FIG. 7, which gives the nomenclature of all these terms used in this specification: Lead Base 183, Foot 185, Heel 187, Twist 189, Stem 191, Taper 193, Pin 195 and End 197, FIG. 7.
Lead or Leg 181, FIG. 7: A connecting element that is provided on an electronic device, to mount the device or
Attach it to another electronic device or a printed circuit board or substrate.
Fold vs. Twist:
I have tried to explain the difference between fold and twist, using words only, and I could not. So, I reverted to using drawings, as in FIGS. 41 and 42.
The sketch in FIG. 41-A shows an elongated flat piece of material, strip 501. The “generatrix” lines 503 that show the form of the strip, along the whole length of the strip, are “parallel” to each other. For example, generatrix 507 anywhere at the right end of the strip is parallel to generatrix 509 at anywhere else along the length of the strip as well as at the left end of the strip.
The sketch in FIG. 41-B shows a “twist”. We start at the right end 511 of the strip, in a similar position as in the sketch, in FIG. 41-A. We will say that the strip at this end is in plane 513. Then we deform the strip for a certain length, and end up at the left end 515 of the strip, where the material now lays in a new plane 517. We will call this new plane, plane 517. We can see two things. First, plane 517 makes an angle “Theta” 519 with plane 513. Second, we see that the generatrix 523 is not parallel to generatrix 521 anymore. Generatrix 523 lays in plane 517 and generatrix 521 lays in plane 513. Thus the angle between generatrix 523 and generatrix 521 is the same “Theta” angle 519, that is the angle between the two planes. The transition between the right end 511 of the strip and the left end 515 is what I call “twist” 525.
The sketch in FIG. 41-C shows a “fold” 531. Here the generatrices are always parallel to each other, regardless of how much we fold the strip.
The sketch in FIG. 42-A shows a strip 541 that starts flat 543, and then it is twisted 545 and then folded 547.
The sketch in FIG. 42-B shows a strip 551 that starts flat 553, and then it is folded 555 and then twisted 557.